A battery is a combination of one or more electrochemical Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity. Batteries may be classified into two categories. Primary batteries irreversibly transform chemical energy to electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical means. Secondary batteries can be recharged. That is, the chemical reactions of the secondary batteries can be reversed by supplying electrical energy to the cell, restoring the original composition of the secondary batteries. Some secondary batteries are not indefinitely rechargeable due to dissipation of the active materials, loss of electrolyte and internal corrosion.